Counterbalanced stair.



' H. KLEINMARK.

GOUNTERBALANGED STAIR.

APPLICATION FILED JULY 5, 1911.

1,018,197. Patented Feb. 20, 1912. I

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UNITED STATES PATENT OFFICE.

HENRY KLEINMARK, OF CHICAGO, ILLINOIS, ASSIGNOR TO J. L. BONDY IRON WORKS 00., OF CHICAGO, ILLINOIS, A CORPORATION OF ILLINOIS.

COUNTERBALANCED STAIR.

Patented Feb. 20, 1912.

Serial No.'636,932.

T 0 all whom it may concern Be it known that I, HENRY KLEINMARK, a citizen of the United States, residing at Chicago, in the county of Cook and State of Illinois, have invented certain new and useful Improvements in counterbalanced Stairs, of which the following is a full, clear, concise, and exact description, reference being had to the accompanying drawings, forming a part of this specification.

My invention relates to counterbalanced stairways, such as are associated with the platforms of fire escapes at a convenient distance above the ground, and its object is to provide an improved stair wherein the proper relation of the parts is maintained in a simple, eflicient and economical manner. It is usual in the art, in the construction of these Stairways, to pivotally mount two side beams or stringers upon a suitable support, and to secure the treads between these side beams or stringers. The stair structure thus formed, of course, extends in but one direction from the pivot means, usually a suitably mounted rod extending from the side of the building, and, in order to counterbalance the stairway to normally keep it off the ground and in a horizontal position, one of the stringersis extended beyond the pivot rod in the opposite direction and is provided with a weight. Since but one of the stringers is thus counterweighted and since the whole stairway is held up in this manner, it follows that there will be a tendency for the other stringer to sag out of transverse alinement and this has been found to be the case wherever provision against it is not made.

It is my intention to provide against the difiiculty pointed out in the preceding paragraph and my invention departs from the general spirit of the braces and other devices heretofore proposed in that it contemplates a peculiar form of tread which, when structurally embodied in the stairway, have stored in them a certain amount of torsional energy which overcomes the undesirable sagging referred to.

My invention is illustrated in the accompanying drawings, in which- Figure 1 is a side elevational view of a counterbalanced stairway embodying my improvement; Fig. 2 is a plan view of one of the specially formed treads; Fig. 3 is an end elevational view of the tread; and Fig.

4 is a side elevational view illustrating the stairway of my invention merely resting upon the ground and not hanging upon a pivot, so as to show the effect of the improved tread formation.

An ordinary fire escape platform is shown at 5, there being a short stationary stalrway portion 6 leading downwardly therefrom. At the bottom of this stairway portion a pivot rod 7 is provided and upon this pivot rod a pair of stringers 8, 8 is mounted. These stringers extend forwardly a distance sufficient so that when the stairway is swung downwardly it may properly reac the ground. The dotted line in Fig. 1 indicates that the remote stringer of the pair does not extend rearwardly beyond the pivot rod 7 any considerable distance. The near stringer 8, however, extends rearwardly for a considerable distance, as illustrated at'9, and, upon this extension, it is provided with a weight. 10, as illustrated. This weight is suflicient to counterbalance the stair structure and to hold it in the raised horizontal position shown in Fig. 1. The outside stringer, the one nearest the eye and having the weight, may be provided with a hand-rail 10' and the front of the stringers may be supplemented by struts 11, 11; with these features, however, my invention has nothing to do.

The front ends of each of the stringers consists of two parallel pieces 12, 12, this arrangement being employed for the purposes of lightness and economy, and between the two stringers the treads 13, 13 are secured. As illustrated in Figs. 2 and 3, each of these treads comprises the two end pieces 14, 14 and a plurality of connecting rods 15, 15 of square cross-section. The relation between these rods and the end pieces is positively determined by mounting the ends of these rods in correspondingly square openings in the end pieces, as best shown in Fig. 3. In the manufacture of these treads, the end pieces 14, 14 are built in intersecting planes, as best shown in Fig. 3, and this may be done by giving the tread a permanent twist as a whole or by twisting each of the connecting rods 15, 15 separately so that they may aggregate the required amount of the offset. The result is that each tread takes the form of the isolated tread shown in the drawings. In assembling the stair each of the treads is fastened in place by securing one of the side pieces 1 1 in place upon one of the stringers. The other side piece of the tread thus secured is then twisted back into the plane of the firstnamed side piece, that is into transverse alinement with it, and, thus being placed under a very considerable torsional strain, it is secured in place to the opposite stringer. The twist which brings the side pieces into parallel relation is in such a direction that the torsional tension which results in the opposite direction will tend to lift the unweighted stringer and to force the counterbalanced stringer downwardly. Referring particularly to the drawings, if the foremost side piece 14: of the tread of Fig. 3 were secured in proper position on the inside of the foremost stringer 8 of Fig. 1, the remote side piece 14 of Fig. 3 would be turned in the direction of the arrows a, a until it came substantially in transverse line with the first-named side piece, and in that posi tion, the remote side piece would be secured to the remote stringer of Fig. 1. The tread, placed under this strain, will tend to raise the short stringer and lower the long one and the result has been found by experiment to be that shown in Fig. 4. It is understood, of course, that practically all of the treads are made and mounted in this way and the aggregate lifting efiect is suflicient to cause the proper amount of primary distortion. \Vhen, however, the stair is hung, the lifting effect will be overcome by gravity and the unbalanced stringer will drop down into approximate alinement with the balanced stringer. It will be understood that the process is simple, since the treads are placed under the required tension by bringing the bolt holes in the side pieces into register with the corresponding bolt holes in the stringers and that the final twisting influence is exerted in each case by the tightening of the bolts.

I claim as new and desire to secure by Letters Patent:

1. In a counterbalanced stairway, a pair of stringers hung upon a pivot, a weight carried by one of said stringers, and treads between said pivot, said treads being placed under torsional strain and being so secured to the stringers as to exert a torsional strain thereon in opposition to the direction of the strain exercised by the weight.

2. In a counterbalanced stairway, a pair of stringers hung upon and extending forwardly from a pivot, one of said stringers having an extension rearwardly from said pivot, a weight on said extension, and treads between said stringers, said treads being placed under torsional strain and being so secured to the stringers as to exert a torsional strain thereon in opposition to the direction of strain exercised by the weight.

3. In a counterbalanced stairway, a pivot rod, a pair of stringers hung upon and extending forwardly from said pivot rod, one of said stringers being extended rearwardly from said pivot rod, a counterweight on said rearward extension, a plurality of treads each comprising side pieces secured to said stringers and a plurality of connecting rods placed under torsional strain in a direction tending ultimately to oppose the direction of strain exercised by the counterweight.

4-. In a counterbalanced stairway, a pair of stringers one of which is counterweighted, and a torsional tread connecting them to ex ert a strain thereon in opposition to the direction of strain exercised by the counterweight.

The herein described process of alin- 'ing a counterweighted stringer and an uncounterweighted stringer in a stairway, which consists in first building twisted treads, then straightening the treads to place them under torsional tension, and securing the treads between said stringers under such torsional strain.

In witness whereof, I hereunto subscribe my name this 1st day of July A. D., 1911. HENRY KLEINMARK. lVitnesses:

ARTHUR H. Bonrrorrnn, LEONARD E. Boson.

Copies of this patent may be obtained for five cents each, by addressing the Commissioner of Patents, Washington, I). C. 

